Human Impact

Salt Water Incursion

Water enters ponds, reservoirs, or wells (our water supply) through groundwater and from surface runoff. Water flows underground between cracks in rocks or pore spaces in soil.

Groundwater fills wells and flows through water bodies like lakes, reservoirs, and the ocean. When we dig a well, where we first hit water is the water table , or the top of the groundwater. The level of the water table varies. It is not flat as its name suggests, but somewhat mimics the topography of the land.

If a lot of water is withdrawn from the groundwater supply for consumption, the level of the water table goes down. When there is a lot of rain or snowmelt, the level of the water table rises. Sometimes it even rises above the ground's surface and floods our yards!

Where sea level is rising, salt water can percolate through sandy soil into coastal wells. As fresh water is pumped out of the wells, salt water replaces it, refilling the wells with undrinkable water.

Show that salt water can replace fresh water in a well along the shoreline

Spread gravel evenly across the bottom of shoe box to a depth of 2-3 inches.

Scoop out a "pond" so its cross-section is along the side of the box facing the students. Scoop another, deeper section on one end of the shoe box to be the "ocean."

Insert the plastic pipe ("the well") all the way to the bottom of the gravel.

Make a small hill and put a plastic house on top.

Fill the shoe box with water halfway up the gravel.

Have one student add water with the spray bottle ("rain") while another removes water with the turkey baster ("using water") to show how the water level changes. When would more water enter well? (spring runoff, snow melt)

When might the well run dry? (summer drought)

Note that the water levels in the pond and the well change at the same rate.

Add more water to the ocean, to simulate sea level rise, and keep withdrawing water from the well as you do this.

As food coloring seeps into the gravel, it eventually shows up in both the pond and the well water. (You may need to add several drops of food coloring). As fresh water is drawn out of the well, salt water moves in to replace it.